Oct. 21, 1886 | 
NATURE 
607 
by conducting their artificial cultivation in a particular way, and 
by transmission through the system of an animal differing in 
nature from that in which the disease naturally occurs. When 
the chain of discoveries reached the point of showing that bacilli 
could be reared outside the body in an artificial soil or culti- 
vating medium, a great advance was made towards obtaining a 
full knowledge about them, as it placed the observer in a more 
favourable position for the successful prosecution of research by 
enabling him to vary and control his conditions in a manner that 
could not otherwise have been effected. Although much has 
been accomplished, it must be said much still remains to be done. 
In the case of a few bacilli the life-history has been pretty clearly 
made out. Cultivated in a certain way they retain their viru- 
lence, no matter through how many successions they pass. The 
last product in a series of successive cultivations is as virulent as 
the parent stock. By modifying the conditions under which the 
cultivation is carried on, the successive products of descent may 
be gradually weakened until they become harmless. Such being 
the case, any desired degree of attenuation may be obtained, and 
by inoculation with a virus brought down to the proper strength 
the non-fatal affection may be occasioned which gives immunity 
from subsequent liability to take the disease under exposure to 
contagion. The knowledge thus acquired has been already 
practically turned to account upon a large scale for checking the 
ravages of that exceedingly fatal disease among cattle known as 
anthrax, or splenic fever, and through the success attained much 
sacrifice of life has been averted. If this can be accomplished 
for one disease, and more than one can be mentioned, is there 
not ground for believing that means will be found for placing others 
of the class in the same position? Attempts are being made in 
this direction. All eyes throughout the civilised world are, 
indeed, at the present moment fixed upon the work of Pasteur 
in Paris with reference to hydrophobia. It would be a great 
achievement for this frightful disease to be brought under sub- 
jection, and certainly the results that have been obtained appear 
to give hopes that an approach to something of this kind has 
been arrived at. Looking at the nature of the disease, there is 
nothing inconsistent with its being dependent upon a bacillus, or 
microbe, as Pasteur calls it. On the contrary, owing its origin 
as it does, when occurring naturally, to inoculation with the 
poisoned secretion of an affected animal, and taking into view 
the facts that have been learnt in connection with its transmission 
by artificial inoculation, evidence points to such in reality being 
the case. If due to a bacillus, why may not this bacillus be 
open to attenuation in the same manner as that of anthrax? If 
thus open to attenuation, why not susceptible of producing a 
non-fatal form of affection? And if this condition has been 
produced and passed through, why should not protection be 
thereby given against the subsequent development of the disease 
as a result of the primary inoculation from the bite of the rabid 
animal? Such a train of reasoning is quite legitimate, and for 
the application of the principle of action to which it leads, there 
is this advantage on the side of hydrophobia, that from the pro- 
longed period usually taken for incubation after the introduction 
of the poison in the ordinary way, time is given for the artificial 
inoculations by subcutaneous injection to produce their effect 
and to render the system refractory to the further development 
of disease. I have been an eye-witness of Pasteur’s work. It 
is from the nerve centre, the seat from which the symptoms of 
the disease start, that he obtains his virus, Employed for in- 
oculation in a fresh state it produces a fatal disease, and the 
disease has been transmitted successively on through a number 
of animals, with the result that the last affected animal yields as 
strong a virus as the first. Kept in a pure, dry air, attenuation 
advances, and after a certain time the nerve centre loses its 
disease-producing power. Used for inoculation at a given period 
of preservation it produces an effect which renders an animal 
resistant to the influence of inoculation with the virus in a fresh 
state, and Pasteur contends that it acts similarly when the virus 
has been introduced in the ordinary way. ‘The treatment of 
persons bitten by rabid animals by inoculation with attenuated 
virus has now been on its trial a considerable time, and a large 
experience gained. Judgment, it must be stated, still stands in 
suspense ; but it must also be said that the results obtained tell 
decidedly in favour of the view advanced. The other method 
by which it has been recently experimentally found that the 
virulence of bacilli can be weakened is by transmission through 
an animal of a different nature from that in which the disease 
naturally occurs. This, in reality, represents the principle at the 
foundation of the system of vaccination, discovered by Jenner at 
the close of the last century. It may now be regarded as an 
accepted conclusion that vaccine-lymph is the virus of small-pox 
modified by transmission through the cow. Jenner's discovery 
consisted in showing that the result of vaccination with the 
lymph of cow-pox affords as much protection against small-pox as 
an attack of small-pox itself. This was the fact he educed, but 
the knowledge possessed in his time did not permit of its being 
looked at in any further way than as a simple fact or truth of 
Nature. Viewed, however, with the light that has been thrown 
upon it by the researches of the present day, we see not only the 
fact, but also its explanation : we see that the principle of action 
of the procedure proposed by Jenner, which has conferred such 
incalculable benefit upon mankind, is based upon the attenuating 
effect upon the small-pox virus of the human species by trans- 
mission through another animal ; and knowing this, the prospect 
is presented of its being rendered susceptible of application for 
the control of other diseases. Whether this should prove so or 
not, at all events advantage is gained by the knowledge acquired. 
Need I say anything more to exhort you, in accordance with the 
duty that has devolved upon me? Surely the acquirement of 
knowledge, giving us as it does greater power in the exercise of 
our calling, and thereby promoting the high and noble object of 
rendering our lives more useful to our fellow-creatures—surely 
this is a sufficient incentive, following the words of Harvey, 
‘to search and study out the secrets of Nature by way of 
experiment,’ ”” 
NOTE ON THE ASTRONOMICAL THEORY OF 
THE GREAT [CE AGE* 
THE following calculation has convinced me that Mr. Croll’s 
theory affords an adequate explanation of the Ice age. I 
compute the total quantity of heat received by each hemisphere 
of the earth during summer and winter respectively as follows :— 
Let 2//a® be the quantity of sun-heat falling perpendicularly 
on an area equal to the section of the earth at the mean distance 
a@ from the sun in the unit of time. 
Let 5 be the sun’s north declination, 
by the northern hemisphere will be 
Then the share received 
Tal ; 
—(I + sin 4), 
ee 
and by the southern 
Let é 
—(1 — sin 4). 
a~ 
At the distance 7, and in the time @, the heat received in the 
northern hemisphere will be 
ye4 : 
(1 + sin 6). a; 
aa) 
but we have 
7°d0 = hat, 
whence the expression becomes 
ree : 
—(1 +sind). a6; 
h 
but we have . 
sin 6 = sin @. sin e, 
where « is the obliquity. 3 
The total heat received by the northern hemisphere from the 
yernal to the autumnal equinox is 
mG Sn, ee : 
/ —(I + sin esin @) . d@0 = —(m + 2 sin e). 
ok h 
We have thus the following theorem :— 
Let 2Z be the total sun-heat received in a year over the whole 
earth ; then this is divided into shares as follows :— 
: m+ 2sine 
Northern hemisphere, summer, car a 
T 
i mw — 2sine 
of winter, £ = 5 
20 
with identical expressions for the summer and winter in the 
southern hemisphere. 
I Paper read at the Royal Irish Academy on May 24, 1886, by Sir Robert 
Stawell Ball, LL.D., F.R.S. Communicated by the Author. 
